According to our knowledge, single-atom Pd catalysts
supported
on covalent triazine frameworks (CTF) have not been studied in the
production of hydrogen from formic acid. Therefore, we synthesized
1 wt % Pd single-atom catalysts based on CTF-1, pyCTF, and bipyCTF
supports and tested them in the gas-phase decomposition of formic
acid. The results were compared with those obtained for a Pd catalyst
supported on mesoporous graphitic-type carbon (Pd/C) with nanoparticles
(∼2.3 nm). The catalysts were characterized by high-angle annular
dark-field/scanning transmission electron microscopy (HAADF/STEM),
extended X-ray absorption fine structure/X-ray absorption near-edge
structure (EXAFS/XANES), and X-ray photoelectron spectroscopy (XPS)
methods. The following order of catalytic activity was obtained: Pd/CTF-1
> Pd/C > Pd/pyCTF ≥ Pd/bipyCTF. The best performance
of the
Pd/CTF-1 catalyst was associated with Pd2+–C2N2 sites. Pd2+–N4 sites
formed on pyCTF and bipyCTF supports showed lower catalytic activity.
The selectivity trend at temperatures above 500 K was as follows:
Pd/bipyCTF > Pd/pyCTF > Pd/CTF-1 > Pd/C. For the Pd/bipyCTF
catalyst,
the selectivity reached 99.8%, which is very high for this temperature
range. These results may be important for the development of CTF-based
catalysts for hydrogen production reactions.